Bone screws are widely used in orthopedic surgical procedures such as spinal surgeries. Typically, bone screws are used to secure structures, such as spinal plates and spinal rod connectors, to various bone portions to stabilize the bone portions relative to others. For example, cervical plates are typically secured to vertebrae with bone screws for stabilization of the cervical spine. Likewise, occipital plates are typically secured to the back of the skull with bone screws for attaching spinal rods.
To attach a bone screw to the bone, the dense outer layers of the bone, or cortical bone, are typically penetrated. The softer inner portions of the bone, or cancellous bone, are typically at least partially penetrated. Various procedures are used to install bone screws. Some include drilling a pilot hole in the bone and tapping the pilot hole to form an internal screw thread before a bone screw is driven into the pre-drilled and pre-tapped pilot hole. Others include driving self-tapping screws into pre-drilled pilot holes. Still others include driving self-drilling screws directly into the bone without pre-drilling or pre-tapping.
In surgical operations, it is generally desirable to minimize the length of time when the surgical wounds remain open and to ensure the quality of the operations. Consistent with this goal, there is therefore a need for bone screws that can be accurately, quickly and securely fastened to bones.